The present invention relates to fluid pressure control systems where it is desired to employ closed loop control utilizing electrically operated valves, and particularly valves of the type operated by a solenoid, for providing pressure control of fluid in a system in response to an electrical signal from an electronic controller.
Solenoid operated valves have found widespread application in systems where it is desired to control fluid pressure to a fluid pressure actuated device such as pneumatic or hydraulically pressure actuated valves, pistons or diaphragms. More particularly, solenoid operated pressure control valves have found widespread use in automotive applications inasmuch as solenoids have proven to be cost effective valve operators capable of energization by the low voltage direct current power supplies typically available on motor vehicles.
An example of the aforesaid automotive applications of solenoid operated pressure control valves is that of utilizing the solenoid operated valve to control the pressure of the hydraulic fluid employed for actuating the shift clutches in an automatic speed change gear set power transmission employed for providing the traction power for vehicle propulsion.
Automatic transmission applications of solenoid operated pressure control valves have heretofore required precise calibration of the solenoid valve to provide the desired pressure output for clutch operation in response to the electrical control signal from the vehicle powertrain controller. In addition, such applications have required extremely tight tolerances on the hysteresis of the valve with respect to valve response from increasing and decreasing electrical control signals. If the valve has a significant amount of hysteresis, or is not repeatable with respect to successive signal applications for the same desired pressure output, the operation of the transmission shift clutches will be jerky or erratic and thus objectionable to the vehicle operator.
The aforesaid problem of accuracy and repeatability of the actuation of an electrically operated pressure control valve operating in an open loop control mode, and particularly solenoid operated valve, irrespective of the application. Thus it has been desired to improve the accuracy and repeatability of solenoid operated pressure control valves for all fluid pressure control applications. Therefore, it has been proposed to use closed loop control mode of operation of solenoid valves.
Published U.S. Application 2004-0122577 published Jun. 24, 2004, assigned to the assignee of the present invention, teaches closed loop control of the shifting of an automatic speed change gear set transmission by utilizing a pressure sensor in the outlet of each solenoid operated pressure control valve for controlling the actuating pressure to the individual shift clutches in the transmission. The pressure sensors in the arrangement of the aforesaid publication are disposed to sense the pressure in the outlet line of the respective solenoid operated pressure control valve to provide a pressure feedback signal to an electronic controller for valve energization and operating the valve in closed loop control of the valve outlet pressure.
Co-pending, commonly assigned U.S. Pat. No. 6,929,031, issued Aug. 16, 2005 and entitled “Electro-Hydraulic Manifold Assembly With Lead Frame Mounted Pressure Sensors” teaches a plurality of solenoid operated pressure control valves mounted in a manifold with a plurality of pressure sensors disposed on an electrical lead frame mounted on the manifold wherein each pressure sensor communicates with the outlet of the individual pressure control valve for sensing the pressure therein.
In co-pending, commonly-assigned U.S Publication No. 2005/0039807, published Feb. 24, 2005 and entitled “Electric Fluid Servo Valve And Method Of Making Same” in the name of Greg E. Ford et al., teaches mounting a pressure sensor on a printed circuit board and attaching the printed circuit board to a valve body of a solenoid operated pressure control valve with the pressure sensor communicating through a sensing port in the valve body with the valve outlet.
The aforesaid closed loop control arrangements for solenoid operated pressure control valves have required that the pressure sensor be externally mounted to communicate with the pressure in the valve outlet and electrically connected separately with the solenoid operator for the valve. In the aforesaid closed loop control arrangements, it is required to install the valve in the hydraulic circuit or a mounting manifold and to provide separate installation of the pressure sensors for communication with the outlet pressure signal from each valve and to connect the pressure sensors and valves separately in an electrical circuit. This has the disadvantage of requiring a separate mounting structure in the hydraulic circuit to provide mounting for the pressure sensors and provision for separate electrical connection thereto which has added significant costs to the arrangement in high volume mass production of motor vehicle automatic transmissions.
Therefore, it has been desired to provide a way or means of sensing the pressure in the outlet of a solenoid operated pressure control valve without separately mounting pressure sensors to the valve or in the pressure outlet line of the valve and to provide such in an easy to manufacture and cost effective manner.